Comcast Corporation said Thursday it is buying Time Warner Cable for more than $45 billion. The deal would create a combined company providing television and Internet services to 30 million customers, who account for about 30 percent of the U.S. pay television market.

The size of the new company could give it wide influence over other media companies, since Comcast already owns the entertainment division of a major U.S. television network, NBC Universal.

The companies said they hope to complete the deal by the end of 2014, but the transaction faces a lengthy review by U.S. regulators.

The two companies currently compete with each other in few markets. Antitrust regulators are likely to look at whether the merged corporation would have too much market share, however, and if it would stifle competing content creators and video companies, such as Netflix.

Public interest groups are protesting the merger. They say that Comcast’s purchase of NBC three years ago has led to higher monthly cable bills for customers.